Polyurethane fiber containing poly(vinylidene fluoride)

ABSTRACT

The present invention relates to polyurethane based fiber containing 0.1-25 percent poly(vinylidene fluoride) and a method of making the same.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to polyurethane-based fibers and, moreparticularly, to spandex containing poly(vinylidene fluoride) forimproved heat-settability and chemical resistance.

2. Discussion of Related Art

Spandex is widely used in apparel such as hosiery, foundation garments,sportswear.

Japanese Patent Application Publication JP07-082608 disclosespoly(tetrafluoroethylene) (“PTFE”) as a compounding agent inpolyurethane ureas prepared from a mixture of MDI and 2,4′-MDI. However,the elongation and tenacity of the spandex suffer as a result.

U.S. Pat. No. 3,751,520 discloses that the blending of poly(vinylidenefluoride) (“PVDF”) into thermoplastic polyurethane reduces thecoefficient of friction of molded polyurethane parts.

Japanese Patent JP63-060156 discloses the application of mixtures ofPVDF and polyurethane to fabrics to form phase-separated coatings.

According to Japanese Published Patent Application 55-084413, PVDFfibers have been melt-spun with the aid of a polyurethane plasticizerwhich is extracted after spinning. However, the use of PVDF to improvethe properties of spandex has not been disclosed.

Reducing the pressure a wearer may feel from a garment containingspandex is generally accomplished by heat-setting the fabric or garment.In order to speed the heat-setting process and save energy, variousmethods have been used to improve the heat-set efficiency of thespandex. These include altering the composition of the spandex by usingselected chain extenders as disclosed in U.S. Pat. No. 4,973,647, andadding certain compounds to the spandex, as disclosed in U.S. Pat. No.5,539,037. However, improved resistance to perspiration and heat-setefficiency are still needed for spandex.

SUMMARY OF THE INVENTION

The composition of this invention is a polyurethane-based fibercontaining 0.1-25 percent poly(vinylidene fluoride), based on the totalweight of polyurethane and PVDF in the fiber.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As used herein, spandex has its customary meaning, that is, amanufactured fiber in which the fiber-forming substance is a long chainsynthetic elastomer comprised of at least 85% by weight of a segmentedpolyurethane. It has now been discovered that both the resistance toperspiration and heat-set efficiency of polyurethane fibers, generally,and spandex, specifically, are unexpectedly and remarkably improved byadding PVDF into the spandex. It is wholly unexpected that two unrelatedcharacteristics can be improved by a single additive, as is the casehere.

In addition, tenacity-at-break, permanent set (which can also be helpfulin reducing the pressure experienced by the wearer) andelongation-at-break are also increased. Furthermore, addition of PVDFinto the spandex did not result in any observed fibrillation of theinventive fiber, nor was the clarity of the fiber affected. Thissuggests that little or no phase separation of the polymers occurs.

For the sake of convenience, the invention herein will be discussed interms of spandex. PVDF is used in the spandex and process of the presentinvention at levels in the range of 0.1-25 percent by weight of totalpolymers, that is polyurethane and PVDF. Preferred levels of PVDF are0.3-15 percent, based on the weight of total polymers in the spandex,with 1-15 weight percent being more preferred.

PVDF suitable for use in the spandex of the present invention issubstantially linear, has a number average molecular weight of300-300,000 as measured by gel permeation chromatography using apolystyrene standard, and has a melt viscosity of 5,000-50,000 poise asmeasured at a shear rate of 50 sec⁻¹ at 240° C. Although PVDF made byeither suspension or emulsion polymerization can be used in the presentinvention, suspension-polymerized PVDF is preferred, because it can formbetter solutions, with less gel.

The spandex of this invention can be made from a polyurethaneureaderived from a polymeric glycol, a diisocyanate, and at least onediamine and/or at least one aminoalcohol, or from a polyurethane derivedfrom a polymeric glycol, a diisocyanate, and at least one diol.

Polyether glycols, polyester glycols, and polycarbonate glycols areuseful in the present invention. Useful polyether glycols includepoly(tetramethyleneether glycol (“PO4G”),poly(tetramethyleneether-co-3-methyl-tetramethyleneether) glycol, andpoly(tetramethyleneether-co-2,3-dimethyl-tetramethyleneether) glycol.Useful polyester glycols include poly-ε-caprolactone diol andhydroxy-terminated reaction products of diols such as ethylene glycol,1,3-propane diol, 1,4-butane diol, 1,6-hexane diol,2,2-dimethyl-1,3-propane diol, 3-methyl-1,5-pentane diol, and mixturesthereof with dicarboxylic acids such as adipic acid, 1,9-nonanedioicacid, and 1,12-dodecanedioic acid. Useful polycarbonate glycols includepoly(pentane-1,5-carbonate) diol and poly(hexane-1,6-carbonate) diol.Such glycols have a molecular weight of about 1000-6000, preferably1500-4500.

Diisocyanates useful in the spandex of the invention include4-methyl-1,3-phenylene diisocyanate,1,1′-methylenebis(4-isocyanatobenzene) (“MDI”),1,4-di-isocyanatobenzene, 1,3-diisocyanatoxylene,1,4-diisocyanatoxylene, 2,6-napthalene diisocyanate,5-isocyanato-1-(isocyanatomethyl)-1,3,3-trimethylcyclohexane,1,1′-methylenebis(4-isocyanatocyclohexane),2,4-diisocyanato-1-methylcyclohexane,2,6-diisocyanato-1-methylcyclohexane, 1,4-diisocyanatocyclohexane, andmixtures thereof. 1,1′-Methylenebis(4-isocyanatobenzene) is preferred.

Depending on whether a polyurethane or a polyurethaneurea is to be made,the chain extender can be a low molecular weight diamine, aminoalcohol,diol, or mixtures thereof. When diamine(s) or aminoalcohol(s) are used,polyurethaneureas are formed. When diol(s) are used, polyurethanes areformed. Useful diamines include ethylene diamine (“EDA”), 1,2-propanediamine, 1,3-propane diamine, 1,6-hexamethylene diamine,1,3-xylylenediamine, N-methylbis(3-aminopropyl)amine,1,4-cyclohexanediamine, 1,3-cyclohexanediamine (“HMPD”),2-methyl-1,5-pentanediamine, 1,3-pentanediamine, and mixtures thereof.Ethylene diamine, 1,2-propane diamine, 2-methyl-1,5-pentanediamine,1,3-cyclo-hexanediamine, 1,3-pentanediamine, and mixtures thereof arepreferred. Suitable low molecular weight diols include ethylene glycol(“2G”), 1,3-propane diol, 1,2-propane diol, 2,2-dimethyl-1,3-propanediol, 1,4-butane diol, 3-methyl-1,5-pentane diol, 1,6-hexane diol,1,4-bis(β-hydroxyethoxy)benzene, N-methylbis(2-hydroxypropyl)amine, andmixtures thereof. Ethylene glycol, 1,3-propane diol, and 1,4-butanediolare preferred.

So long as the advantages of the present invention are not diminished,small amounts of ingredients of greater than difunctionality can beused, such as diethylenetriamine.

The polyurethane used in making the spandex has a number averagemolecular weight of 40,000-150,000 as measured by gel permeationchromatography using a polystyrene standard, and a high-temperature-sidemelting point of 200°-260° C. as measured on a second cycle bydifferential scanning calorimetry. In order to control the molecularweight of the polyurethane, small amounts of a monofunctional chainterminator such as diethylamine can be added.

The spandex can contain additives such as stabilizers and pigments,provided such additives do not detract from the benefits of theinvention. Among such additives are benzotriazole based stabilizers,ultraviolet light absorbers, other light resistance agents,antioxidants, anti-tack agents, lubricants such as mineral oil andsilicone oils, antistatic agents. Other examples of additives includehindered phenolic stabilizers such as 2,6-di-t-butyl-4-methyl-phenol asa light stabilizer, antioxidants such as “Sumilizer” GA-80 (SumitomoKagaku Kogyo KK), benzotriazoles including a variety of “Tinuvin”stabilizers (Ciba Specialties), phosphorus chemicals such as “Sumilizer”P-16 (Sumitomo), nitrogen oxide traps such as HN-150 (Nippon Hydrazine),light stabilizers such as “Sumisorb” 300#622 (Sumitomo), hindered aminestabilizers including various “Tinuvin” types, inorganic pigments suchas titanium oxide, zinc oxide, and carbon black, metal salts such asmagnesium stearate and barium sulfate, hydrotalcite, mixtures of huntiteand hydromagnesite, bactericides containing silver, zinc, or compoundsthereof, deodorants, a variety of anti-static agents, cerium oxide, andphosphoric acids.

In the process of the present invention, either dry-spinning ormelt-spinning can be used to make the spandex. To make polyurethanes formelt-spinning, either melt-polymerization or solution polymerization canbe used, and the polymerization can be carried out in one step or twosteps. PVDF can be added to the polyurethane as a finely divided solid,and the resulting spinning mixture, optionally containing otheradditives as described herein, can be melt-spun to form the spandex.

When the spandex of the present invention is to be prepared bydry-spinning, a two-step solution polymerization process can be used,especially for polyurethaneureas. In two-step solution polymerization,the polymeric glycol is contacted with the diisocyanate, the mole ratio(“capping ratio”) of diisocyanate to glycol being about 1.5-4.5, to forma mixture of isocyanate-terminated glycol and unreacted diisocyanatewhich mixture is designated a “capped glycol”. The capped glycol isdissolved in a suitable solvent such as dimethylacetamide (“DMAc”),dimethylformamide, dimethylsulfoxide, and N-methyl-pyrrolidone. DMAc ispreferred. To the resulting solution of capped glycol is added at leastone chain extender and a small amount of chain terminator to form thepolyurethane(urea). (For polyurethanes, a one-step solutionpolymerization process can also be used, in which the polymeric glycol,diisocyanate, and at least one diol chain extender are added to thesolvent substantially simultaneously.) Optional stabilizers and pigmentscan be added to the resulting solution, which has a polyurethane(urea)content of at least 30 weight percent. In the process of the presentinvention, PVDF and optionally stabilizers, pigments, and the like, canbe added and mixed thoroughly into the polymer solution to form aspinning mixture which is a solution. The spinning solution can then bespun through a spinneret into a heated column in which the solventevaporates from the polymer to form the spandex, which can then be woundup.

When diol-extended polyurethanes are to be made, it can be advantageousto use one or more polymerization catalysts. Typical amine catalystsinclude N,N-dimethylcyclohexylamine, N,N-dimethyl-benzylamine,triethylamine, N-methylmorpholine, N-ethylmorpholine,N,N,N′,N′-tetramethylethylene diamine, N,N,N′,N′-tetramethyl-1,3-propanediamine, N,N,N′,N′-tetramethylhexane diamine, bis-2-dimethylamino ethylether, N,N,N′,N′,N″-pentamethyldiethylene triamine, tetramethylguanidine, triethylene diamine, N,N′-dimethyl piperazine,N-methyl-N′-dimethylamino ethyl-piperazine, N-(2-dimethylamino ethyl)morpholine, 1-methyl imidazole, 1,2-dimethyl imidazole,N,N-dimethylamino ethanol, N,N,N′-trimethylamino ethyl ethanol amine,N-methyl-N′-2-hydroxy ethyl (piperazine, 2,4,6-tris(dimethylaminomethyl) phenol, N,N-dimethyamino hexanol, and triethanol amine.Organometallic polymerization catalysts include tin octanoate,dibutyltin dilaurate,and dibutyl lead octanoate.

Any suitable equipment can be used for adding and mixing PVDF into thepolyurethane(urea) solutions. Typical equipment includes static mixers,stirrers, homogenizers, and screw extruders. PVDF can be added as asolution in the same solvent used to make the polyurethane(urea)solution, or it can be added as a finely divided solid.

In order to attain higher tenacity, the dry-spinning speed is at least450 meters per minute. In the spandex and process of the presentinvention, no drop in polyvinylidene fluoride content or yarndiscoloration was observed due to the heat experienced in dry spinning.

Percent set and percent stress-relaxation of the spandex of thisinvention are sensitive to the ratio of the speed of the windup to thatof the Godet roll, which is 1.15-1.65. If a high set, lowstress-relaxation yarn is desired, the ratio can be 1.15-1.40,preferably 1.15-1.35. If a low set, high stress-relaxation yarn isdesired, the ratio can be 1.25-1.65, preferably 1.35-1.65.

The analytical tests used to characterize the spandex prepared in theExamples were performed as follows.

The viscosity of the polyurethane(urea) solutions was determined inaccordance with the general method of ASTM D1343-69 with a Model DV-8Falling Ball Viscometer, (sold by Duratech Corp., Waynesboro, Va.),operated at 40° C. The percent set, percent stress-relaxation, tenacity,and percent elongation were obtained by testing the spandex with anInstron Model 4502 tensile tester.

A 5-cm (length L1) spandex sample was stretched to 300% elongation at aspeed of 50 cm/min and then allowed to relax. This cycle was repeatedfive times. Stress was measured at the end of the fifth stretch anddesignated G1. The sample was then held at 300% elongation for 30seconds, after which stress was again measured and designated G2. Thepercent difference between G1 and G2 was reported as the percent stressrelaxation. The sample was then allowed to relax from the fifth stretchuntil the stress was zero; the length at this point was measured anddesignated L2. The percent difference between L1 and L2 was reported asthe percent set. The sample was stretched a final, sixth time until itbroke. The stress at the break was measured, designated the tenacity,and reported in grams. The length at break was also measured anddesignated L3, and the percent difference between L1 and L3 wasreported,as percent elongation. These relationships are furtherdescribed by the following equations:

% Stress-relaxation=100×((G1)−(G2))/(G1)

% Set=100×((L2)−(L1))/(L1)

% Elongation=100×((L3)−(L1))/(L1)

To determine heat-set (percent), the fiber was treated in a relaxedcondition for 10 minutes with 100° C. steam, treated in a relaxedcondition for 2 hours with boiling water, and dried at room temperaturefor one day. The relaxed length was measured and designated L4. Thefiber was then extended 100%, treated with 115° C. steam for 1 minute,and subsequently treated with 130° C. air for 1 minute at the same 100%extension. Next, the fiber was left to stand at 100% extension at roomtemperature for one day. The fiber was then allowed to relax, and thefinal length (L5) was measured. The percent heat set was calculated fromthe following equation:

% Heat set=100×((L5)−(L4))/(L4)

To simulate the exposure of spandex to body oils and perspiration, thefiber was held at 100% elongation for 24 hours in a 5% by weightsolution of oleic acid in hexane, followed by holding it (still at 100%elongation) for 1 hour in an 0.5% by weight solution of N,N′-diethyltoluamide in ethanol. The fiber was then dried for 24 hours at roomtemperature in a relaxed condition. Elongation at break of the treatedfiber was measured on the sixth extension and designated E1. The ratioof the elongation at break of the treated fiber to the elongation atbreak of untreated fiber (E2) was used as a measure of chemicalresistance.

% Chemical resistance=100×(E1)/(E2)

The amount of PVDF in the spandex was determined analytically asfollows. First, a calibration curve was prepared for each type of fiber,as classified by chain extender. One gram of fiber was rinsed withn-hexane and completely dissolved in 50 ml of DMAc to form apolyurethane solution. Then, 100 ml of ethanol was gradually added toprecipitate the PVDF, which was filtered from the solution anddiscarded. The filtered polyurethane solution was evaporated to dryness.DMAc solutions of the residue and 0%, 1%, 3%, 6%, 10%, and 20% by weightof PVDF, based on the total weight of polyurethane and PVDF, wereprepared. Films were prepared by casting the solutions and analyzed byFourier-Transform InfraRed. Ratios (“Xc”) of infra-red peak areas at ν(CO) 1700cm⁻¹-1800cm⁻¹ compared to the peak areas at ν (CF₂) 890cm⁻¹were obtained for each of the films with a Perkin-Elmer FT-IR. Acalibration curve, having a slope (α), was prepared by plotting the wt %PVDF content against the peak area ratio (Xc).

To determine the amount of PVDF in a fiber test sample, the fiber wasrinsed with n-hexane, dissolved in DMAc, cast into a film and its IRspectrum determined. The ratio (Xs) of the peak area at ν (CO)1700cm⁻¹-1880cm⁻¹ compared to the peak area at ν (CF₂) 890cm⁻¹ of thespectrum of the film was obtained. The wt % PVDF in the fiber sample wasdetermined by comparing Xs to the calibration curve:

Weight % PVDF=(α)×(Xs)

EXAMPLES

In the Examples, for polyurethanes in which the chain extender wasethylene glycol, the windup speed was 540 m/minute and the ratio of thewindup speed to the Godet roll speed was 1.40 (Examples 1, 2, 3, and 4,and Comparative Examples 1 and 2). For polyurethaneureas in which thechain extender was ethylene diamine (Example 5 and Comparative Example3), the windup speed was 600 m/min, and the winder/Godet speed ratio was1.20. The windup speed was 600 m/min and the winder/Godet speed ratiowas 1.30 for polyurethaneureas in which the chain extender was an 80/20mole ratio mixture of ethylene diamine and 1,3-cyclohexane diamine(Example 6 and Comparative Example 4). The spandex was 18 denier (20dTex) in all Examples, and its high-side melting point was 229°-258° C.

“Zokki” style (with spandex in every course) pantyhose was knitted usingthe spandex of the invention (Examples 1, 2, 3, 4, 5, and 6) which hadmachine sizes greater than, and wear pressure lower than, those ofconventional “Zokki” pantyhose using spandex not of the invention buthaving the same knitting tension and knit construction. The spandex ofthe invention produced “Zokki” pantyhose having excellent wear comfortand easy donning and doffing.

Example 1

PO4G having a molecular weight of 2900 (496 grams) and MDI (170 grams,capping ratio 3.97) were stirred together for 2 hours at 80° C. to forma capped glycol. Dry DMAc (1333 ml) was added, and the mixture wasstirred to dissolve the capped glycol. Then 2G chain extender (37.87grams) was added and the resulting mixture was stirred for 6 hours and60° C., followed by addition of n-butanol chain terminator (14.16grams). The resulting solution was 35% by weight polyurethane and had afalling ball viscosity (“FBV”) of 4000 poise. A 2050-g quantity of thepolyurethane solution was mixed with 222 g of a 10 wt % solution of acommercial PVDF, number average molecular weight, 48,000, meltviscosity, 12,000 poise (Kureha Chemical Company, Tokyo, Japan) in DMAc,and the resulting solution was agitated for 2 hours. As stabilizingadditives, 11.1 grams of a 2:1 by weight mixture of a condensationpolymer of p-cresol with divinyl benzene (described in U.S. Pat. No.3,553,290) and a polymer of bis(4-isocyanatocyclohexyl)methane withN-t-butyldiethanol-amine (3-t-butyl-3-aza-1,5-pentanediol) (described inU.S. Pat. No. 3,555,115) were added to the polyurethane/PVDF solution.The resulting solution was agitated for 2 hours and then conventionallydry spun to give a spandex of the invention whose properties are shownin Table I.

Example 2

To 2000 g of a polyurethane solution prepared as in Example 1 was added216 g of a DMAC solution (10% by weight) of a commercial PVDF (Kureha,number average molecular weight, 72,000, melt viscosity, 47,000 poise),followed by agitation for 2 hours. 11.8 grams of an additive mixture asdescribed in Example 1 was added, and the solution was agitated foranother 2 hours. The resulting solution was conventionally dry spun toform a spandex of the invention whose properties are reported in TableI.

Example 3

To 2000 g of a polyurethane solution prepared as described in Example 1was added 70 g of a DMAC solution (5% by weight) of PVDF used in Example2, followed by thorough agitation for 8 hours using a homogenizingblender. To the resulting solution was added 10.6 g of an additivemixture as described in Example 1, and the solution was agitated for 2hours and then conventionally dry-spun to give a spandex of theinvention whose properties are shown in Table I.

Example 4

To 2000 g of a polyurethane solution prepared as described in Example 1was added 1975 g of a DMAc solution (10% by weight) of the same PVDF aswas used in Example 2. The solution was agitated for 2 hours, and then13.5 g of an additive mixture as described in Example 1 was added andmixed thoroughly for another 2 hours. The solution was conventionallydry-spun to obtain a spandex of the invention whose properties arereported in Table I.

Comparative Example 1

To 2000 g of a polyurethane solution prepared as described in Example 1was added 10.5 g of an additive mixture as described in Example 1,followed by agitation for 2 hours. The solution was then conventionallydry-spun to give a spandex outside of this invention. Properties areshown in Table I.

Comparative Example 2

Into 2000 g of a polyurethane solution prepared as described in Example1 was added 22 g of polytetra-fluoroethylene (PTFE, Teflon® K-10,particle size 0.2 micron, DuPont-Mitsui Fluorochemical Company, Tokyo,Japan) using a homogenizing mixer. 10.8 g of the additive mixturedescribed in Example 1 was added, and the mixture was agitated for 8hours. The mixture was dry-spun to form a spandex outside of theinvention. Properties are also shown in Table I.

TABLE I Stress- Chemical PVDF Elongation Tenacity Relaxation Heat-setResistance Example (wt %) (%) (grams) Set (%) (%) (%) (%) 1 0.5 410 2130 35 61 72 2 3.0 430 22 33 35 65 85 3 3.0 425 23 32 35 64 87 4 22.0 40521 44 40 69 88 Comp. 1 0.0 405 20 25 35 55 56 Comp. 2 PTFE: 370 17 27 3752 59 3.1

As can be seen from Table I, the chemical resistance andheat-settability of spandex of this invention are increased over spandexcontaining no PVDF or even when containing PTFE (but no PVDF), withoutmaterially affecting the stress relaxation. Within the more preferredrange of 1-20% by weight of PVDF, percent elongation and tenacity arealso improved, and percent set is increased without becoming excessive.

“Zokki” style pantyhose made from the spandex of Examples 1, 2, 3, and 4were soaked for 24 hours in a hexane solution of oleic acid (5% byweight) followed by washing and drying. A wear test of the treatedpantyhose showed that their durability was 1.3 times (1.4 times in thecase of Example 4) that of “Zokki” style pantyhose made from the spandexof Comparative Example 1 (outside of this invention).

Example 5

Capped glycol was prepared by mixing 704 grams PO4G (1800 molecularweight) and 155 grams MDI (capping ratio 1.58) for 2 hours at 80° C. DryDMAc (1625 ml) was added, and the mixture was stirred to dissolve thecapped glycol. A mixture of ethylene diamine (13.76 grams) and diethylamine (2.01 grams) was added, and the mixture was stirred for anadditional hour at 60° C. The resulting solution contained 35 wt %polyurethaneurea and had an FBV of 2500 poise. To 2500 g of thepolyurethaneurea solution was added 659 g of a DMAc solution (10% byweight) of the same PVDF as used in Example 1, and the solution wasstirred for 2 hours. 14.1 g of the additive mixture described in Example1 was added, followed by agitation for 2 hours. The solution wasconventionally dry-spun to give a spandex of the invention whoseproperties are shown in Table II.

Comparative Example 3

To 2500 g of a polurethaneurea solution prepared as described in Example5 was added 13.1 g of the additive mixture described in Example 1,followed by agitation of the solution for 2 hours and then conventionaldry-spinning to produce a spandex outside of this invention. Propertiesare given in Table II.

TABLE II Stress- Chemical PVDF Elongation Tenacity Relaxation Heat-setResistance Example (wt %) (%) (grams) Set (%) (%) (%) (%) 5 7.0 520 2831 28 45 90 Comp. 3 0.0 490 25 18 28 25 60

As can be seen from Table II, tenacity, heat-settability, and chemicalresistance of spandex of this invention, based on polyurethaneurea whichhas been chain extended with ethylene diamine, show unexpectedimprovement over spandex outside of the invention, containing no PVDF.

Example 6

A capped glycol was prepared from 687 grams of PO4G (1800 molecularweight) and 166 grams MDI (capping ratio 1.74) by mixing for 2 hours at80° C. Dry DMAc (1625 ml) was added, and the mixture was stirred todissolve the capped glycol. An 80/20 mole ratio of ethylene diamine(15.12 grams) to 1,3-cyclohexyldiamine (3.78 grams) chain extenders and2.68 grams diethylamine chain terminator were added, and the mixture wasstirred for one hour at 60° C. The resulting solution contained 35% byweight polyurethaneurea, and its FBV was 2900 poise. To 2500 g of thissolution was added 155 g of a non-commercial, experimental PVDF powderobtained from Kureha, number average molecular weight 5,000, and themixture was thoroughly mixed with an homogenizer. To the homogenizedsolution was added 15.5 g of the additive mixture described in Example1, followed by agitation for 2 hours. The solution was conventionallydry-spun to provide a spandex of this invention having the propertiesshown in Table III.

Comparative Example 4

To 2000 g of a polyurethaneurea solution prepared as described inExample 6 was added 13.5 g of the additive mixture described in Example1, followed by agitation for 2 hours. The resulting solution wasconventionally dry-spun to give a spandex outside of the invention.Properties are shown in Table III.

TABLE III Stress- Chemical PVDF Elongation Tenacity Relaxation Heat-setResistance Example (wt %) (%) (grams) Set (%) (%) (%) (%) 6 15.0 525 2530 30 60 96 Comp. 4 0.0 500 22 22 30 30 62

As can be seen from Table III, spandex of this invention, based onpolyurethaneurea prepared with a mixture of chain extenders andcontaining PVDF, has improved heat-settability and chemical resistanceover a similar spandex outside of this invention which does not containPVDF.

Pantyhose prepared from the spandex of Example 6 was soaked for 24 hoursin a hexane solution of oleic acid (5% by weight) followed by washingand drying. A wear test of the treated pantyhose showed that itsdurability was 1.2 times that of similarly treated pantyhose made withthe spandex outside of this invention (Comparative Example 4).

What is claimed is:
 1. A polyurethane-based fiber containing 0.1-25percent poly(vinylidene fluoride) (PVDF), based on the total weight ofpolyurethane and PVDF in the fiber.
 2. The fiber of claim 1 containing0.3-15 weight percent poly(vinylidene fluoride).
 3. The fiber of claim 1which is spandex.
 4. The spandex of claim 3 wherein the poly(vinylidenefluoride) has a number average molecular weight of 300-300,000 and amelt viscosity at 240° C. of 5,000-50,000 poise.
 5. The spandex of claim3 wherein the spandex is derived from a polymeric glycol selected fromthe group consisting of polyether, polycarbonate, and polyester glycols,a diisocyanate, and at least one difunctional chain extender selectedfrom the group consisting of ethylene diamine, 1,2-propane diamine,1,3-propane diamine, 1,3-cyclohexanediamine,2-methyl-1,5-pentanediamine, 1,3-pentanediamine, 1,3-xylylenediamine,N-methylbis(3-aminopropyl)amine, ethylene glycol, 1,3-propane diol,1,4-butane diol, 1,2-propane diol, 2,2-dimethyl-1,3-propane diol,3-methyl-1,5-pentane diol, 1,6-hexane diol,1,4-bis(β-hydroxy-ethoxy)benzene, and N-methylbis(2-hydroxypropyl)amine.6. The spandex of claim 5 wherein the polymeric glycol is a polyetherselected from the group consisting of poly(tetramethyleneether) glycoland poly(tetramethyleneether-co-3-methyltetramethyleneether) glycol, andthe diisocyanate is 1,1′-methylenebis(4-isocyanatobenzene).
 7. Thespandex of claim 5 wherein the polymeric glycol is a polyester derivedfrom diols selected from the group consisting of ethylene glycol,2,2-dimethyl-1,3-propane glycol, 1-methyl-1,2-ethane diol, 1,3-propanediol, 1,4-butane diol, 3-methyl-1,5-pentane diol, 1,6-hexane dial, andmixtures thereof, and diacids selected from the group consisting ofadipic acid, 1,9-nonanedioic acid, and 1,12-dodecanedioic acid, and thediisocyanate is 1,1′-methylenebis(4-isocyanatobenzene).
 8. The spandexof claim 3 containing 0.5-15 weight percent poly(vinylidene difluoride).9. A process for making polyurethane-based fiber comprising the stepsof: (a) preparing a polymer selected from the group consisting ofelastomeric segmented polyurethanes and polyurethaneureas; (b) adding0.1-25 weight percent, based on the total weight of polymer and PVDF, ofpoly(vinylidene fluoride) to the polymer to form a spinning mixture; and(c) spinning the mixture to form the fiber.
 10. The process of claim 9wherein the fiber is spandex.
 11. The process of claim 10, wherein thepolymer is derived from a polymeric glycol selected from the groupconsisting of polyether, polycarbonate, and polyester glycols, adiisocyanate, and at least one difunctional chain extender selected fromthe group consisting of ethylene diamine, 1,2-propane diamine,1,3-propane diamine, 1,3-cyclohexanediamine,2-methyl-1,5-pentanediamine, 1,3-pentanediamine, 1,3-xylylenediamine,N-methylbis(3-aminopropyl)amine, ethylene glycol, 1,3-propane dial,1,4-butane diol, 1,2-propane diol, 2,2-dimethyl-1,3-propane diol,3-methyl-1,5-pentane diol, 1,6-hexane diol,1,4-bis(β-hydroxyethoxy)benzene, and N-methylbis(2-hydroxypropyl)amine;wherein the spinning mixture is a spinning solution; and wherein thesolution is dry-spun to form spandex.
 12. The process of claim 10wherein the polymer is derived from a polymeric glycol selected from thegroup consisting of polyether-, polycarbonate-, and polyester glycols, adiisocyanate, and at least one difunctional chain extender selected fromthe group consisting of ethylene glycol, 1,3-propane diol, 1,4-butanediol, 1,2-propane diol, 2,2-dimethyl-1,3-propane diol,3-methyl-1,5-pentane diol, 1,6-hexane diol,1,4-bis(β-hydroxyethoxy)benzene, and N-methylbis(2-hydroxypropyl)amine;wherein the spinning mixture is substantially free of solvent; andwherein the solution is melt-spun to form spandex.